One of the basic objections against time travel is, that it is against our intuition that
time is a single straight line without break or branching point and against our common-sense
belief that a thing is occupying a single place at a moment in time and it cannot be in two
places at the same time.
Thinking about physical time travel almost unavoidable leads to the dreaded
"Grandfather Paradox":

You go back in time and kill your grandfather before your parents were born. Thus,
if your parents are never born, you could never be born. But if you were never born,
you couldn't have killed your grandfather. But if you hadn't killed your grandfather,
you would've been born. And so on.

Bottom line, however, is that paradoxes do not exist: they are the product of our mind.
In our case, it might be the consequence of trying to apply time travel to the wrong
theory on time.
Our current theory does not allow for time travel.
If we however insist using the classic model and imagine the consequences
of traveling to the past, paradoxes will immediately pop up.

The multiverse theory presumes that every change in the past,
creates a new universe and is one of the theories that evades the obvious time travel paradox.
However since paradoxes do not exist they do not need not to be avoided.

A multiple universe theory, allowing travelers to alter the past, without risk
of endangering their own history time line, would be an open invitation for an invasion
of 'experts from the future' who know it all better, without them having to bear the
consequences of their own actions. There is no evidence in our own history that something
similar ever happened.